This invention relates generally to pipettes and the fabrication thereof. More specifically, it relates both to a novel method for the manufacture of multi-barrel glass micropipettes and to the micropipettes themselves.
One of the major uses of multi-barrel glass micropipettes is in research testing procedures where it is necessary to test the response of living matter, such as cells, or tissue, to certain chemical stimuli. A detailed illustration of this type of procedure is presented in Microelectrophoresis, Chapter 4, by David R. Curtis, and a copy of that chapter is being submitted with the accompanying Prior Art Statement. Basically, fluids containing different substances are loaded into the different barrels of the micropipette. The micropipette is then used to dispense minute amounts of the fluid-carried substances with suitable accuracy and efficiency so as to enable many different substances to be expeditiously tested on many different types of living matter, as desired.
The micropipette apparatus that is described by Curtis in the above reference comprises a multi-barrel glass micropipette that comprises a number of individual glass tubes that are bundled together side-by-side and tapered to a dispensing tip at the distal end of the micropipette. Each tube oonstitutes an individual barrel that is loaded with a particular fluid-carried substance via the end that is opposite the tip. The configuration of a straight central tube around which the remaining tubes are circumferentially arranged, is convenient both for dispensing substance-containing fluids from the micropipette, and for loading the fluids into the barrels, especially where the inlet ends of the surrounding tubes are canted outwardly, as shown in the Curtis Article.
However, the manner of fabricating the micropipettes of the Curtis article is relatively time-consuming, involving considerable amounts of hand labor. Hence, this contributes to the cost of producing a micropipette. For example, the individual tubes of a bundle are cut to length from straight tubes, they are formed as required to create the basic desired shape for each, they are bundled side-by-side along their distal end portions and finally the bundled distal end portions are softened by heating and then drawn to a taper. Upon cooling, the distal end portion of the micropipette is broken off and discarded as scrap yielding a single multi-barrel micropipette in which each individual tube has its own very tiny dispensing orifice at the distalmost end of the micropipette. Curtis comments on the difficulty of breaking off the distal end portion (bumping the tip) to produce a desired minute orifice size.
It has become a practice in the industry for the micropipettes to be fabricated as "blanks" which are shipped from the manufacturer to the customer. The blanks have the basic micropipette shape, as described, but the distal ends have not been "finished" to yield the desired dispensing orifice sizes. The customer has equipment to perform the finishing by re-drawing the tapered tip so that it will conform to the customer's particular needs.
Since such finishing involves heating and axially elongating the distal end portion of the mioropipette, it is necessary for axial elongating forces to be applied to the micropipette. The customer has apparatus for performing the finishing, typically a machine that has a pair of axially aligned chucks that face each other. The axial ends of the micropipette are grabbed by the respective chucks, and when the distal end portion of the micropipette has been suitably softened, the chucks are moved relatively away from each other to perform the re-drawing.
One of the difficulties in performing such a finishing procedure involves grabbing the necked-down distal end portion by the corresponding chuck. Too much radial force may break the glass, yet an insufficient force will not satisfactorily hold the glass. Because it comes to a tip, the distal end is difficult to grab, and therefore, additional prepping of the tip is virtually mandatory. For example, shrink tubing is often inserted over the tip forming a sleeve that grips the tip for pulling. Nonetheless, such a procedure still results in a significant amount of breakage.
It is known to provide what are called "prepulled blanks" in which the necked-down taper is created in the middle of the bundled tubes. An example of such a blank is shown in the publication entitled "Multibarrel Micropipettes" referred to in the accompanying Prior Art Statement. The distal end of the bundle is the same diameter as that lying to the axially opposite side of the taper, and both distal and proximal ends of the bundle contain ferrules, or metal rings, secured to the glass via which the blank is chucked for re-drawing. While a prepulled blank of this form may provide lesser difficulty in re-drawing of the taper, it is wasteful of material because a large mass of glass is broken off and discarded as scrap after the re-draw, and only one micropipette is produced. Hence, there is a need for improvement upon the procedures that have been described, and such improvement is offered by the present invention.
The present invention, in one principal aspect, relates to a novel method for manufacturing a multi-barrel micropipette with improved efficiency. Basically, the method is effective to create two micropipettes from an individual manufacturing operation. The resulting product can be produced at a lower cost than the micropipette that is described in the Curtis article and this benefit can ultimately be passed on to the consumer. While the invention still involves steps of assembling glass tubes together and drawing tapers, it does so in a novel and unique way.
Moreover, according to another principal aspect of the invention, a new step is added to the procedure of fabricating a micropipette which comprises creating a bulbous shape at the distal end of the dispensing tip. This enlarged bulbous shape facilitates the handling and usage of the micropipette by the customer, especially for customer finishing of the tipped end.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at the present time in carrying out the invention.